1. Field of the Invention
The present invention is in the field of position measurements, and more specifically, is in the field of improving the quality of position measurements.
2. Discussion of the Prior Art
In the prior art, there are several methods of improving position measurements by performing the operations of filtering and/or smoothing of obtained position measurements. The prior art also discusses different ways of improving measurements by performing sensor fusion, that is by combining a number of measurements performed by a plurality of sensors in order to obtain a higher quality position measurement as compared with a position measurement obtained by a single sensor. For instance, the well known in the art Kalman filter significantly increases the accuracy of Global Position System (GPS) position measurements by combining Global Position System (GPS) measurements and the Inertial Navigation System (INS) measurements.
However, the prior art methods of improving the quality of position measurements do not teach how to improve the quality of position measurements of an object in a situation when a previously available source of high quality position measurements becomes unavailable, and only a low quality source of position measurements is available.
What is needed is a method for substituting a high quality source of position measurements with a low quality source of position measurements when a previously available source of high quality position measurements becomes unavailable, while minimizing the degradation in quality of position measurements due to switch from the high quality source of position measurements to the low quality source of position measurements.
To address the shortcomings of the available art, the present invention provides a method for substituting a high quality source of position measurements with a low quality source of position measurements when a previously available source of high quality position measurements becomes unavailable.
One aspect of the present invention is directed to a method for substituting at least one high quality position measurement with a set of upgraded low quality position measurements. In one embodiment, the method comprises the following steps: selecting a high quality source of position measurements of an object; obtaining at least one high quality position measurement of the object obtained by using the high quality source; wherein at least one high quality position measurement of the object includes a high quality epoch timing coordinate indicative of when the high quality position measurement of the object was taken; wherein a threshold of acceptability is defined as a bound between an xe2x80x9cacceptablexe2x80x9d error in a position measurement of the object and an xe2x80x9cunacceptablexe2x80x9d error in the position measurement of the object; and wherein the high quality position measurement of the object includes the acceptable error in the high quality position measurement of the object; and wherein each high quality position measurement of the object satisfies the threshold of acceptability requirement for the object; saving at least one high quality position measurement of the object taken at at least one high quality epoch timing coordinate; selecting a low quality source of position measurements of the object; and obtaining at least one low quality position measurement of the object using the low quality source; wherein at least one low quality position measurement of the object includes a low quality epoch timing coordinate indicative of when at least one low quality position measurement of the object was taken.
In one embodiment of the present invention, if at least one high quality position measurement of the object is available and substantially recent, the method of present invention further includes the step of using at least one high quality position measurement of the object for navigation purposes of the object. In this embodiment, the high quality measurement is available if the source of high quality position measurements is generating a stream of high quality position measurements, and the high quality position measurement is unavailable if the source of high quality position measurements stops generating the stream of high quality measurements. The high quality position measurement is substantially recent if a rate of updating the high quality position measurement is substantially sufficient to obtain a substantially accurate position measurement of the object.
If, on the other hand, each high quality position measurement of the object is unavailable, or is available but is not substantially recent, the method of present invention further includes the following steps: upgrading at least one low quality position measurement of the object by using at least one high quality position measurement of the object to obtain at least one upgraded low quality position measurement of the object; and using at least one upgraded low quality position measurement of the object in place of at least one high quality position measurement for navigation purposes of the object, if the upgraded low quality position measurement of the object being considered satisfies the threshold of acceptability requirement for the object.
In one embodiment, the method of the present invention for substituting at least one high quality position measurement with a set of upgraded low quality position measurements further includes the step of setting the threshold of acceptability of the error in the position measurement of the object. In one embodiment of the present invention, the threshold of acceptability of the error in the position measurement of the object is set to be a standard deviation of a set of position measurement errors taken over a statistically significant time period. In another embodiment of the present invention, the threshold of acceptability of the error in the position measurement of the object is set to be a maximum measurement error that is acceptable for a given navigation application of the object.
In one embodiment of the present invention, the step of selecting the high quality source of position measurements further includes the step of providing the high quality source of position measurements selected from the group consisting of: {a carrier differential SATPS; a code differential SATPS; an autonomous SATPS; an Inertial Navigation System (INS) having a high accuracy (HAINS); a high quality source including the HAINS and the carrier differential SATPS; a high quality source including the HAINS and the code differential SATPS; and a high quality source including the HAINS and the autonomous SATPS}.
In one embodiment of the present invention, the step of selecting the low quality source of position measurements of the object further includes the step of providing the low quality source of position measurements selected from the group consisting of: {a carrier differential SATPS; a code differential SATPS; an autonomous SATPS; and an Inertial Navigation System (INS) having a low accuracy (LAINS)}.
Another aspect of the present invention is directed to a method for substituting at least one high quality position measurement with a set of upgraded low quality position measurements, wherein there are a plurality of sources of low quality measurements are available. In one embodiment, the method of the present invention comprises the following steps: selecting at least one high quality source of position measurements of an object; obtaining at least one high quality position measurement of the object by using at least one high quality source of high quality position measurements; saving at least one high quality position measurement of the object at at least one high quality epoch timing coordinate; selecting at least one low quality source of position measurements of the object; and obtaining at least one low quality position measurement of the object by using at least one low quality source.
In one embodiment of the present invention, if at least one high quality position measurement of the object obtained by at least one high source position measurement is available and substantially recent, the method of the present invention further includes the step of using at least one high quality position measurement of the object for navigation purposes of the object. In this embodiment, the high quality measurement is available if at least one source of high quality position measurements is generating a stream of high quality position measurements, and wherein the high quality position measurement is unavailable if each source of high quality position measurements stops generating a stream of high quality measurements.
In one embodiment of the present invention, the step of using at least one high quality position measurement of the object for navigation purposes of the object further includes the steps of: periodically checking whether at least one high quality position measurement of the object is available and is substantially recent; and if at least two of the high quality position measurements of the object are available and are substantially recent, selecting a highest ranked high quality position measurement of the object having a highest rank, and using the highest ranked high quality position measurement of the object for navigation purposes.
The highest ranked high quality position is obtained by using a highest ranked source of high quality measurements, wherein the highest rank is selected from the group consisting of: {a highest frequency at which the high quality position measurements are provided; a lowest standard deviation of errors of the high quality position measurements; a lowest maximum expected error of the high quality position measurements; and a highest likelihood of availability of the high quality position measurements}.
If, on the other hand, at least one high quality position measurement of the object is unavailable, or is available but is not substantially recent, the method of the present invention further includes the steps of: of upgrading at least one low quality position measurement of the object by using the most recently saved high quality position measurement of the object; and using at least one upgraded low quality position measurement of the object in place of the of high quality position measurement of the object for navigation purposes, if the upgraded low quality position measurement of the object satisfies the threshold of acceptability requirement for the object.
In one embodiment of the present invention, the step of selecting the low quality source of position measurements of the object further includes the step of selecting a highest ranked low quality source of position measurements of the object. The highest ranked low quality source outputs at least one highest ranked low quality position measurement of the object, wherein the highest rank is selected from the group consisting of: {a longest substitution period; wherein the substitution period is a period of time during which each upgraded highest rank low quality position measurement is expected to satisfy the threshold of acceptability requirement; a lowest standard deviation of errors of the low quality position measurements during the substitution period; and a lowest maximum expected error of low quality position measurements during the substitution period}.
Yet, one more aspect of the present invention is directed to an apparatus for substituting at least one high quality position measurement with a set of upgraded low quality position measurements. In one embodiment, the apparatus comprises: a means for selecting a high quality source of position measurements of an object; a high quality source configured to obtain at least one high quality position measurement of the object; a means for saving at least one high quality position measurement of the object taken at at least one high quality epoch timing coordinate; a means for selecting a low quality source of position measurements of the object; a low quality source configured to obtain at least one low quality position measurement; and a processor.
In one embodiment of the present invention, the processor includes an algorithm comprising at least the following steps: (a) upgrading at least one low quality position measurement of the object by using at least one saved high quality position measurement of the object to obtain at least one upgraded low quality position measurement of the object; and (b) if each high quality position measurement of the object is unavailable, or is available, but is not substantially recent; and if each upgraded low quality position measurement of the object satisfies the threshold of acceptability requirement for the object, substituting at least one high quality measurement of the object with at least one upgraded low quality position measurement of the object.